The present invention relates to an image processor used for reproducing a continuous tone image such as a photograph as black-and-white binary dot image (i.e. halftone image).
In a conventional image scanner/recorder, a tone scale (i.e., gray scale) of a read out digital image signal is roughly corrected by an operator's skill during signal processing so as to assure tone quality of the output image. No attempt has, however, been made to automatically obtain linear tone scale conversion.
Along with recent developments in electrophotographic and printing techniques, even in the conventional image scanner/recorder, there arises a strong demand for highly precise tone reproduction. Therefore, conventional trial-and-error methods must be greatly improved. The most significant improvement is to realize a system for assuring linear tone scale conversion between an input image and the output image. More particularly, in the linear tone scale conversion system, a precise tone change in an input image must be controlled in accordance with a tone correction curve without trial-and-error. Then, in the scanner/recorder having the linear tone scale convention, an operator can easily control the tone quality of the output image without sensous skill.